Current transformer



Nov. 26, 1929 E. M.. CLAYTOR AET AL CURRENT TRANSFORMER Filed Feb. l, 1927 2 Sheets-Sheet 1 lNvENToRS Edward McroeClo yor and Harold E.Cobb. da@ BY ATTORNEY y Nov. 26, 1929. E. M. CLAYTOR' l- TL 1,736,994'

CURRENT TRANSFORMER Filed Feb. l, 1927 2 Sheets-Sheet 2l Flg 537 IPIII UUIHNWNIIIHIHNIHIUH ai lit- Vy 2bl IUIiIIIIIIIIIIIIIlIIIIIINIIHII lNvENToRS Edward Merce CloyTorand Hd rold fOobb.

7 ATTRNEY Patented Nov. 26, 1929 UNITED STAT-ES PATENT OFFICE EDWARD M. CLAYTOR, OF EDGEWOOD ACRES, AND HAROLD COBB, OF WILKINSBURG, PENNSYLVANIA, ASSIGNORS TO W'ESTINGHOUSE ELECTRIC AND MANUFACTURING COMPANY, A CORPORATION 0F PENNSYLVANIA CURRENT TRANSFORMER Application filed February 1, 1927. Serial No. 165,097.

Our invention relates to current transformers and particularly to core constructions therefor.

One object of our invention is to provide a current transformer that shall be adapted for use with electrical devices having differ`- ent current ratings.

Another object of our invention is to provide a current transformer that shall be especially adapted for use in connection with thermal relays.

Another object of our invention is to provide a current transformer that shall be adapted for use in connection with circuits for large motors having large starting moments of inertia and long starting periods.

A further object of our invention is to provide a current transformer that shall be adapted for detachable mounting on a panel board.

Heretofore, standard instrument trar formers having 1vound primary win-dii vs and wound secondary windings have been connected in electric circuits for operating thermal relays. rThe primary winding of a transformer of the character above specified carries the entire load current of the circuit and, from the secondary winding, a reduced current is imparted to the heating element of the thermal relay. If the percent overload of the primary current be plotted against the percent overload of the secondary current, for such transformer, the resultant curve will be that of a straight line. These transformers are costly to build and are not easily mounted upon a panel or bus-bar.

In our invention, we provide a primary winding with a core that, by its construction, makes it possible to obtain a time-delay effect from the secondary Winding. The core is constituted by an assemblage of sheet-metal laminations some of or all of which have .radial slots of predetermined width formed Fig. l is a view, partially in elevation and partially in section, of a current transformer embodying our invention;

Fig. 2 is a face view of a lamination having a slot therein constituting a detail of our in vention;

Fig. 3 is a diagrammatic view of circuits and thermal-relay apparatus embodying our invention Fig. i is a view illustrating the saturation curve for a standard instrument transformer and a characteristic operating curve of a current transformer embodying our invention;

Figs. 5, 6 and 7 are views similar to Figs. l, 2 and 3, respectively, of a modified forni of our invention.

Referring to Figs. l, 2, 3 and 4, our invention comprises, in general, a current transformer 1 having a primary winding 2 which may be a single conductor mounted on a switch panel 3, and a core member 4 that surrounds the primary winding conductor 2.

The primary winding 2, in the example shown is a threaded stud, one end of which may be provided with a contact terminal that can be tightened against the front surface of the switch panel 3 by a nut 5. The core memw ber 4 is secured to the stud by the combination of sleeve 6 and nuts 7 and 8. Nuts 9 provide means for attaching a primary terminal thereto.

The core member i may be either an asn semblage of slotted laminations 10 or a combination of slotted and unslotted lan'iinations. Metallic terminal side plates 11 and 12 are connected to the primary conductor 2 on opposite sides of the core member t, as by means of the conducting nut 7 and the conducting sleeve and nut 6 and 8. The side plates 11 and 12 may be clamped to the core member by threaded rods 15 and nuts 16 and are insulated from the laminations 10 by nonmetallic sleeves 17 and fibre washers 18. The end laminations 10"t are preferably thicker than the laminations 10 for securing mechanical support.

rEhe perforated lamination 10 is shown in Fig. 2 as having a slot or air gap 19 of any desired width for opening its magnetic circuit. Holes 21 are provided for the reception of sleeves 17, which prevent circulating currents from being set up in the core member 4;.

In operation, the primary Winding 2 is connected in series relation to the motor circuit, as shown in Fig. 3. The presence of the core member 4 around the primary Winding 2 which carries alternating current, causes a voltage drop across the space which it covers. A shunted or secondary current that lags the primary current by a phase angle of 90 is taken from the terminal plate members 13 and 111 and passed through the heating element 22 of thermal relay 23.

The shunted or secondary current depends upon the number of the perforated laminations 10, the Width of the slots 19, and the staggered relation of the slots 19 to one another. By combination of these diversifications, an overload current may be made to follow any desired operating curve A-B, shown in Fig. l, i diere primary ratings along the abscissa are plotted against secondary ratings along the ordinate. The line AC is thc saturation curve, when unslotted laminations are used throughout, as is the case With the instrument type current transformers heretofore employed.

Referring to Figs. 5, 6 and 7, a modified form of our invention comprises, in general, a current transformer 25 having a single-turn primary Winding 26, a core member 27 surrounding the primary Winding and a secondary Winding 28 inductively related to the primary Winding 26.

rl `he primary Winding 26 is a threaded stud to which the terminals 29 and 31 are attached and held fixed against steel plates 32 anc 33 that bear, respectively, on the sides of the core by nuts 311 and 35.

The core member 27 is an assemblage of slotted laminations. rFliese laminations are sustained by bolts 37 extending through sleeves 38 and nuts 39. The perforated lamination l1 is shown in Fig. 6 as having a slot 37 across one side.

The secondary Winding 28 passes through the steel plates 32 and 33 and around one side of the core member 27. Any number of turns may be employed.

In operation, a primary current passes through the primary Winding 26 Which is inductively related to the secondary Winding 2S from which a secondary current is passed to the heating element of a thermal relay.

The manner in Which the laminations are disposed is the same for this current transformer 25 as heretofore set forth in connection with the description of the current transformer 1.

Accordingly, our invention provides a method for obtaining a time delay in the operation of thermal relays, by varying the impedance of al transformer that is simple in construction, inexpensive to manufacture and is easily mounted upon a panel or a bus-bar.

It is understood that various modifications and changes may be made in the invention Without departing from its spirit and scope, as set forth in the appended claims.

7e claim as our invention:

1. In an instrument transformer, a conductor, means for mounting the conductor, a magnetic core member surrounding the conductor comprising a combination of slotted and unslotted laminations,

2. ln an instrument transformer, a conductor, means for mounting the conductor, means for attaching a terminal to the conductor, and magnetic core member surrounding the conductor and comprising a group of slotted laminations and a group of unslotted lam inations.

3. ln a current transformer, a primary Winding having means for attaching terminal members thereto, and a metallic core member surrounding said primary Winding and comprising groups of slotted Washers and groups of unslotted Washers.

ln combination, a bus-bar having means for attaching terminal plate members thereto7 a metallic core member surrounding the bus-bar and interposed and in proximity to the terminal members and comprising a combin ation of slotted and unslotted laminatious.

5. ln a current transformer, a conductor, means for mounting the conductor, means for attaching terminal members to the conductor, a m agnetiI/.able core member surrounding the conductor and comprising t,roups of slotted laminations and unslotted laminations, any tivo of said groups spaced by a single unsiotted lamination, and the slots of adjacent laminations disposed in unaligned positions.

in testimony whereof, We have hereunto subscribed our names this 26th day 0f January, 1927.

EDVARD M. CLAYTOR. HAROLD E. COBB. 

